This invention relates to a data transmitting/receiving apparatus, and more specifically, to a radio communication apparatus and a radio communication method which can transfer data at high-speed using simple circuitry.
Recently, communication methods using spread spectrum (SS) techniques in which the band range of a modulated signal is made significantly wider than that of the signal using narrow-band modulation have been utilized in the field of radio communication such as mobile communication. This is because the communication methods using the spread spectrum techniques are characterized by (1) resistance to jam, (2) resistance to interference, (3) strong security and the like. Direct Sequence (DS) and Frequency Hopping (FH) are well known as methods for generating a spread signal by use of the spread spectrum. In the Direct Sequence method, for example, the spectrum of a signal to be transmitted is spread by use of pseudo-random codes named spreading code (Pseudo-random Noise (PN) code).
In the spread spectrum communication method using the spreading code, data to be transmitted are subjected to primary (1st) modulation and then to secondary (2nd) modulation. The modulated signal is then transmitted from an antenna. On the other hand, a signal received by the antenna is subjected to de-spreading and demodulation, whereby the data are restored. For accomplishing the above mentioned primary modulation, Phase Shift Keying (PSK), Differentially encoded PSK (DPSK), Quadrature PSK (QPSK) or the like is utilized, thereby multiplying the primarily modulated digital signal by the PN code series to obtain the spread signal. On the other hand, the signal received by the antenna on the receiving side is multiplied by the PN code series.
In the spread spectrum communication method, as mentioned above, the band range of the modulated signal is significantly larger than that of the signal using the narrow-modulation, and therefore, the S/N ratio on the front end of the receiving side is quite low. Accordingly, it is not easy to detect and decode the signal. In addition to this problem, a timing for generating the PN code at the receiving side is different from a timing for generating the PN code at the transmitting side. Accordingly a receiving circuit which accomplishes the above mentioned method is provided with special circuitry to execute two processing operations, namely acquisition and tracking, so as to suitably receive the signal and recognize what the signal means correctly.
For accomplishing this, the front portion of the data series to be transmitted (the header) is provided with a special signal (preamble) for the acquisition. Also, the conventional receiving circuit includes a digital matched filter (DMF) to execute the acquisition, while it executes the tracking by sampling the output from the DMF at a higher frequency than a spreading ratio and reviewing the adjacent peaks output from the matched filter so as to adjust the next sample timing.
In this way, the conventional receiving circuit includes dedicated circuits for the acquisition (such as DMF) and tracking. These dedicated circuits are complicated, which means that the communication apparatus has to be large-scaled. Further, if the wave strength is lowered when receiving a data series, it may be impossible to accomplish the acquisition. In this case, it is impossible to receive the signal suitably until the acquisition is again executed by use of the preamble in the following data series.
Incidentally, the aspect in which a plurality of users use a common band is called multiple access. As multiple access methods, there are known Frequency Division Multiple Access (FDMA) which uses distinct frequencies (communication channels) for every user, Time Division Multiple Access (TDMA) which uses the same frequency but assigns distinct time slots for every user, and Code Division Multiple Access (CDMA) which uses the spreading code.
In TDMA, since a radio communication apparatus is assigned to a time slot, the radio communication apparatus transmits a necessary signal in the assigned time slot, while another radio communication apparatus at the receiving side receives the signal transmitted in the assigned time slot. Accordingly, it is necessary to manage time information when using the TDMA. A conventional communication system is provided with a base station as well as radio communication apparatuses (slave stations), and the base station transmits the time information to each radio communication apparatus thereby adjusting transmitting/receiving timing of each radio communication apparatus. Alternatively, each radio communication apparatus may comprise a timer keeping the same time, and transmit the prescribed signal in its own assigned time slot based on the timer.
In the former, however, it is necessary to provide a separate base station capable of communication to each radio communication apparatus (slave station). Further since it is difficult to increase the number of slave stations, the system becomes restricted or inflexible. In addition thereto, if one base station can not transmit the time information to all radio communication apparatuses (slave stations), it is impossible to make use of the communication system unless another base stations are provided. On the other hand, since the speed at which a signal propagates through a transmission path has recently become very high (e.g. 2xcx9c5 Mbps), in the latter it is actually impossible to adjust the timer so as to keep the same time in each radio apparatus.
In view of the above, the object of the present invention is to provide a radio communication apparatus having simple circuitry and capable of accomplishing suitable synchronization, and a transmitter and a receiver constituting the radio communication apparatus.
Another object of the present invention is to provide a communication system using TDMA in which the communication apparatuses can suitably communicate with each other without providing a dedicated base station.
The above mentioned and other objects of the present invention are accomplished by a radio communication apparatus using spectrum spread, comprising a transmission circuit which generates modulated signals by use of primary modulation and spreading of data to be sent, and a receiving circuit which obtains data by use of de-spreading and demodulation of received signals, the apparatus comprising a data divider which divides the data to be sent into a plurality of data rows each having a prescribed length, and a data generator which receives the data rows and generates data sets each including a prescribed preamble and the data row, wherein the transmission circuit repeatedly transmits the data sets each including the preamble and data row, and wherein the receiving circuit receives the data sets and captures a portion of the received signal which corresponds to the preamble to accomplish acquisition.
The above mentioned and other objects of the present invention are also accomplished by a radio communication apparatus using spectrum spread and comprising a transmission circuit including a primary modulator which subjects data to be sent to primary modulation and a spread circuit which subjects the primarily modulated data to the spectrum spread so as to generate and transmit modulated signals, and a receiving circuit which subjects received signals to de-spreading and demodulation so as to restore data, the apparatus comprising a buffer which temporarily stores the data to be sent, and input processor which generates a preamble and outputs it to the primary modulator, and thereafter, reads from the buffer a data row having a prescribed length and outputs it to the primary modulator, wherein the transmission circuit repeatedly transmits data sets each including the preamble and the data row supplied from the input processor, and wherein the receiving circuit receives the data sets and captures a portion of the received signal which corresponds to the preamble to accomplish acquisition.
According to the present invention, the transmission circuit repeatedly transmits the data sets each including a portion corresponding to the preamble and another portion corresponding to the data row, while the receiving circuit accomplishes the acquisition using the repeatedly supplied portion corresponding to the preamble. Accordingly, since the acquisition is executed at a prescribed interval, it is possible to appropriately receive the data body and restore it without executing symbol tracking.
In a preferred aspect of the present invention, the prescribed length of the data row is determined based on an error between a clock speed or clock frequency used in the transmission circuit and another clock speed or clock frequency which is expected to be used in a destination receiving circuit. More preferably, the prescribed length of the data row is equal to or less than Tsyn/(2xe2x80xa2dT), wherein dT=|1/Ftxxe2x88x921/Frx|, Tsyn=1/Ftx, Ftx is a clock frequency used in the transmission circuit, and Frx is a clock frequency expected to be used in the destination receiving circuit. According to this aspect, at the destination side, the appropriate acquisition can be accomplished, at least preventing errors in data interpretation owning to the margin of error between the clocks of the transmission and receiving sides.
Besides, the above mentioned and other objects of the present invention are accomplished by a transmission apparatus corresponding to the above mentioned transmission circuit or a receiving apparatus corresponding to the above mentioned receiving circuit, or a transmission method corresponding to an operation of the transmission circuit or a receiving method corresponding to an operation of the above mentioned receiving circuit.
Furthermore, the objects of the present invention are accomplished by a radio communication apparatus which transmits and receives data in one or more time slots using TDMA, comprising a first time slot number obtaining circuit which receives signals and, based thereon, obtains at least one time slot number which is used by another station which is communicating with yet another, a timer which measures a time concerning the time slot; and a transmission time calculation circuit which calculates a starting time of its own time slot based on the obtained time slot number and the time, wherein the apparatus transmits its own time slot number and the data to be sent at the calculated starting time.
According to this aspect, based on the time slot number and its time information (e.g. starting time) concerning the other station, the starting time of its own time slot is calculated in a reverse manner. Accordingly, without providing a base station for managing time or keeping the same time among the radio communication stations, it is possible to appropriately transmit signals in the own slot.
The time slot may be assigned in advanced or may be dynamically assigned by searching for vacant slots. In the latter, it is preferable to provide the apparatus with a vacant slot detector which finds out at least one vacant slot number based on the obtained slot number to select its own slot number from among the found vacant slot numbers.
In a further preferable aspect of the present invention, the apparatus further comprises a primary map which stores a first list indicative of time slot numbers of other stations which are communicating with another, and a secondary map which stores a second list indicative of time slot numbers used by secondary stations, the secondary stations being further stations which the other stations recognize as being communicating, and the time slot numbers of secondary stations being obtained and transmitted to the apparatus by the other stations, wherein the vacant slot detector finds out the vacant slot number based on the first and second lists in the primary and secondary maps.
According to this aspect, the apparatus can find out the time slot numbers used by the further stations which the apparatus itself can not directly communicate with. In view of this, it is possible to prevent collision owing to interference of the time slot with other stations.
In order to prevent the above mentioned collision, the radio communication apparatus may further comprise a tertiary map which stores a third list indicative of time slot numbers used by tertiary stations, the tertiary stations being still further stations which the secondary stations recognize as being communicating, and the time slot numbers of third stations being obtained and transmitted to the apparatus by the secondary stations via the other stations, wherein the vacant slot detector finds out the vacant slot number based on the first, second and third lists in the primary, secondary and tertiary maps. The above objects are accomplished by a radio communication method comprising the above mentioned features.
Furthermore, the present invention can provide a digital cord-less telephone apparatus comprising radio communication apparatuses using the above mentioned TDMA method.